Control mechanism for model airplanes

ABSTRACT

Radio control model aircraft achieve trim by an offset to the transmitted signal. The offset is generally set by a slider control. A remote control transmitter, is disclosed having a first input device for providing an input signal to which the transmitter is responsive to provide a control signal to control proportionally an operating parameter of a controlled apparatus. The input device has a neutral state, in which the input signal has a value of zero, corresponding to a desired neutral value of the operating parameter. Operation of a second input device causes the transmitter to provide an offset to the control signal in the same sense as any input to the first input device. The offset increases in value until the first input device is in its neutral state when the operating parameter has the neutral value. In the exemplary application, when the aircraft is flying straight and level, the second input device, which may be a push button, is operated. The pilot continues to fly the aircraft straight and level. In doing so the stick input required reduces until the stick is in the neutral position. The increase in the value of the offset preferably takes place at a rate commensurate with the pilot remaining in control throughout.

[0001] This invention relates to control mechanisms, e.g. radio control transmitters.

[0002] The background to the invention will be explained in relation to radio control transmitters used for controlling model aircraft. The reader may appreciate that the invention is applicable to other applications.

[0003] Almost all aircraft are provided with trimming devices which are used to offset the control surfaces so that the controls, e.g. stick and rudder bar, are in neutral positions when the aircraft is flying straight and level. The requirement to trim the controls is also present in model aircraft. Radio control model aircraft achieve the trim by an offset to the transmitted signal. The offset is generally set by a slider control. In general, the transmitter has input devices in the form of one or more joysticks. The aircraft is flown straight and level and the sliders are set so that this can be achieved with neutral stick input. Setting the sliders requires a degree of practiced skill, to the extent that when a model pilot is learning, an instructor will generally trim the aircraft before handing control to a pupil. Further, setting the sliders is not possible, or at least is not easy, with the hand that is controlling the associated stick and, especially, in the case of three channel control, e.g. aileron, elevator and rudder, at least on channel is left uncontrolled while the sliders are set for the other(s).

[0004] Against this background, in accordance with the invention, there is provided a remote control transmitter, comprising a first input device for providing an input signal to which the transmitter is responsive to provide a control signal to control proportionally an operating parameter of a controlled apparatus, the input device having a neutral state, in which the input signal has a value of zero, corresponding to a desired neutral value of the operating parameter; and a second input device operation of which causes the transmitter to provide an offset to the control signal in the same sense as any input to the first input device, said offset increasing in value until the first input device is in its neutral state when the operating parameter has the neutral value. In the exemplary application, when the aircraft is flying straight and level, the second input device, which may be a push button, is operated. The pilot continues to fly the aircraft straight and level. In doing so the stick input required reduces until the stick is in the neutral position. The increase in the value of the offset preferably takes place at a rate commensurate with the pilot remaining in control throughout.

[0005] In one form, the transmitter is responsive to the first input signal having a value less than a predetermined amount different from zero, to hold the value of the offset.

[0006] Another form includes means responsive to operation of the second input device to store the contemporaneous value of the input signal and is operative to provide an offset to the value of the control signal which increases in the same sense as the stored value until the effect of the offset differs by less than a predetermined amount from that corresponding to the stored value.

[0007] In a most preferred form the transmitter is a radio transmitter, the controlled apparatus is a model aircraft and the parameter is the position of a control surface thereof.

[0008] The invention also extends to a mechanism for controlling the orientation of one or more control members the orientation of which determines the attitude or direction of a vehicle, the mechanism having: a first input member which is manually movable in position and biased to a neutral position, the mechanism being arranged to control the orientation of the control member(s) dependent on the position of the input member; a detector for detecting that the position of the input member is not neutral, and a trimmer responsive to operation of a second input member to provide an offset to the control member(s) in a sense determined by the position of the input member, said offset increasing in magnitude until the position of the input member is neutral.

[0009] The bias may be provided by, for example, springs so that the neutral position is fixed. In operation the vehicle is controlled so that its direction or attitude is that which it is desired should correspond to the neutral position of the input member, for example in the case of an aircraft: straight and level. Presuming the vehicle to be out of trim, requiring non neutral input from the first input member, when the second input member, which may be a push switch, is operated, a gradually increasing offset is given to the orientation of the control member(s). The offset is in a sense to reduce the input required from the first input member until it reaches its (fixed) neutral position.

[0010] In an alternative, the bias may be provided by the control members. That is to say changing their orientation from a neutral one requires force which is reflected at the first input member. In, for example, motorcars, this is called “feel” at the steering wheel. In this case the vehicle is again controlled so that its direction or attitude is that which it is desired should correspond to the neutral position of the input member, for example in the case of an aircraft: straight and level. Presuming the vehicle to be out of trim, requiring non neutral input from the first input member, when the second input member is operated, the first input member remains in the same position as the offset increases, until the position of the first input member becomes the neutral position.

[0011] Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0012]FIG. 1 is a schematic of a radio control transmitter embodying the invention;

[0013]FIG. 2 is a schematic of another radio control transmitter embodying the invention; and

[0014]FIGS. 3 and 4 are block diagrams useful in explaining operation of the transmitters of FIGS. 1 and 2 respectively.

[0015] Referring to FIG. 1 of the drawings, a radio control transmitter 2 is used to control the flight of a fixed wing model aircraft 4. The aircraft has control surfaces in the form of ailerons 6, for controlling roll, elevators 8 for controlling pitch, and a rudder 10 for controlling yaw. The transmitter has three separate channels: one for controlling the ailerons, one for controlling the elevators and one for controlling the rudder. Only one channel is illustrated in FIG. 1. For the sake of example, consider that the illustrated channel controls the elevators 6.

[0016] The transmitter 2 has an input device in the form of a joy stick 12. Movement of the joystick 12 in one plane, the plane of the paper as illustrated, positions the wiper 14 of a potentiometer 16 to control the ailerons. Movement of the stick 12 in a plane perpendicular to the paper in FIG. 1 would generally control another parameter, e.g. elevator position or engine speed, depending on the mode of operation. The potentiometer is connected between a voltage reference +V_(ref) and −V_(ref) so that the analog voltage appearing on the wiper 14 is dependent on its position and thus on the position of the stick 12 in the plane of the paper. The stick has a neutral position to which it is biased and in which the voltage on the wiper is zero. The voltage on the wiper constitutes an input signal to an analog to digital converter 18 and the digitised voltage is input to a processor 20.

[0017] The processor 20 converts the digitised voltage to a standard pulse position (PPM) control signal or pulse code (PCM) control signal which is modulated onto a carrier by a modulator 24 and transmitted via an antenna 26 to the model 4. The model demodulates the signal received to obtain a control signal to control a servo which positions the ailerons as is known.

[0018] If the pilot feels the model is not trimmed properly, i.e. requires stick input to fly straight (in the case of the ailerons) s/he operates a second input device in the form of a push button 28. This signals the processor to begin a trim routine. In the trim routine, the processor provides a gradually increasing offset to the value of the PPM or PCM control signal in the same sense as the stick input. Thus if the stick input is left because the model tends to fly to the right, the value of the offset gradually increases in a sense to turn the model to the left. The pilot continues to fly the model level and in doing so gradually decreases the stick input commensurate with the increasing offset. During the process illustrated in FIG. 3, the processor compares the digitised control output of the analog to digital converter 18 with a digital reference representing the neutral position of the stick (zero volts). When the two are within a predetermined difference, e.g. zero digital difference, the processor ceases increasing the value of the offset and holds the current value. This results in the model being trimmed in roll.

[0019] Separate processes are provided for all three channels. Each may be started by its own push button, or two or all processes may be started simultaneously by a common pushbutton.

[0020] The embodiment shown in FIG. 2 is different in having a hold circuit 30 responsive to operation of the push button 28 to hold the digitised output of the analog to digital converter 18. The routine instigated by operation of the push button illustrated in FIG. 4, begins outputting an increasing offset in the same sense as the output of the hold circuit 30. As the magnitude of the offset increases, it is compared with the output of the hold circuit and when the two differ by less than a predetermined amount, e.g. zero digital difference, the increase ceases and the processor 20 holds the current offset. This results in the offset having the same effect as the input signal had at the moment it was stored in the hold circuit 30, so that the model is trimmed in roll.

[0021] The increases in offset take place at a rate slow enough for the pilot to accommodate. The rate itself may be set, or the time period over which the change takes place may be set. 

1. A remote control transmitter, comprising a first input device for providing an input signal to which the transmitter is responsive to provide a control signal to control proportionally an operating parameter of a controlled apparatus, the input device having a neutral state, in which the input signal has a value of zero, corresponding to a desired neutral value of the operating parameter; and a second input device operation of which causes the transmitter to provide an offset to the control signal in the same sense as any input to the first input device, said offset increasing in value until the first input device is substantially in its neutral state when the operating parameter has the neutral value.
 2. A transmitter as claimed in claim 1, which is responsive to the input signal having a value less than a predetermined amount different from its zero to state hold the value of the offset.
 3. A transmitter as claimed in claim 1, including means responsive to operation of the second input device to store the contemporaneous value of the input signal and operative to provide an offset to the value of the control signal increases in the same sense as the stored value until the effect of the offset differs by less than a predetermined amount from that corresponding to the stored value.
 4. A transmitter as claimed in claim 1 or 2, wherein the controlled apparatus is a model aircraft and the parameter is the position of a control surface.
 5. A mechanism for controlling the orientation of one or more control members the orientation of which determines the attitude or direction of a vehicle, the mechanism having: a first input member which is manually movable in position and biased to a neutral position, the mechanism being arranged to control the orientation of the control member(s) dependent on the position of the input member; a detector for detecting that the position of the input member is not neutral, and a trimmer responsive to operation of a second input member to provide an offset to the control member(s) in a sense determined by the position of the input member, said offset increasing in magnitude until the position of the input member is neutral. 